Reference is made to the commonly assigned U.S. Patent Applications, the respective disclosures of which being incorporated herein by reference:
(1) U.S. application Ser. No. 09/474,352, filed on Dec. 29, 1999 and entitled xe2x80x9cApparatus for Positioning Work Stations in a Document Printer/Copierxe2x80x9d.
(2) U.S. application Ser. No. 09/574,054, filed concurrently herewith and entitled xe2x80x9cPin Mount for Optical Writer/Recording Element in a Document Printer/Copierxe2x80x9d.
(3) U.S. application Ser. No. 09/574,275, filed concurrently herewith and entitled xe2x80x9cCantilever Drum Mount for Document Printer/Copierxe2x80x9d.
(4) U.S. application Ser. No. 09/574,447, filed concurrently herewith and entitled xe2x80x9cImage Transfer Drum for Document Printer/Copierxe2x80x9d.
The present invention relates to field of document printing and copying. More particularly, it relates to improvements in methods and apparatus for precisely positioning the various work-stations of a document printer/copier, e.g., an electrophotographic printer, relative to (i) the photosensitive surface of an image-recording drum on which toner images are formed, and, optionally, (ii) the non-stick (abhesive) surface of an intermediate image-transfer drum to which toner images are transferred from the image-recording drum before being ultimately transferred to an image-receiver sheet.
Automated electrophotographic copiers and printers have been known for nearly fifty years. Copiers and printers differ only from an input standpoint, copiers being adapted to receive hard copy input, whereas printers are adapted to receive an input in electronic form, e.g., from a computer terminal. Both carry out the basic electrophotographic imaging process of uniformly charging a photoconductive layer with electrostatic charge, imagewise exposing the charged layer to radiation adapted to discharge the layer, thereby leaving behind a latent charge image, and applying pigmented electroscopic particles (toner) to the charge image to render it visible. Most often, the toner image so formed is transferred to a receiver sheet whereupon the toner image is permanentized by heat and/or pressure. Optionally, for example, to extend the lifetime of the photoconductive recording element, the toner image formed on the image-recording drum is transferred to an intermediate transfer drum or the like before it is again transferred to the receiver sheet. In the case of full color copying and printing, multiple color-separated toner images (e.g., cyan, magenta, yellow and black) are produced by the above process and transferred in registration to a receiver sheet.
Since the inception of electrophotographic printers/copiers, the xe2x80x9choly grailxe2x80x9d for many manufacturers has been to produce images of photographic quality, both monochromatic and full color. As will be appreciated, the quality of a full color image is determined not only by the respective qualities of each of the color-separated toner images formed on the photoconductive recording element(s), but also by the degree with which such images can be transferred from the recording element(s) and brought into perfect registration on the image receiver sheet. Such image quality of the color-separated images and the registration thereof, in turn, depend in large part upon the precision with which the various work-stations or subsystems that carry out the electrophotographic process can be physically placed relative on the surface of the recording element. Thus, various schemes have been proposed and used in the past that address this technical problem.
While focusing on image-quality and registration issues, printer manufacturers are ever mindful of lowering manufacturing and service costs. Thus, substantial efforts have been made to simplify service and maintenance procedures so that the need for service calls by highly trained technicians and specialists can be minimized. Ideally, for example, all of the major workstations of the printer, e.g. the charging, exposure, development, transfer and cleaning stations, as well as the recording element itself, should be replaceable by the end user or customer with no sacrifice being made to the ultimate image quality. Even where the services of a trained technician are required, the time to implement such replacements should be minimal. The achievement of this goal not only requires that each of the printer work-stations be modularized so as effect a xe2x80x9cplug and playxe2x80x9d concept, but also requires that a very precise and highly reliable work station-registration scheme be designed so that each work station, upon being removed from the printer frame for servicing and/or replacement, can be returned to within a few microns of its nominal position. In the case of high quality color printing, the respective placements of the printer workstations is particularly critical and skilled servicing personnel are usually required to make the major sub-system changes. Obviously, the need for service assistance should be minimized.
In the above-referenced U.S. application Ser. No. 09/474,352, a work station registration scheme for an electrophotographic printer is disclosed in which a plurality of dowel pins on the printer frame serve to locate both a photoconductive drum assembly and an image transfer drum assembly. Each drum assembly comprises a pair of drum-support members, commonly referred to as xe2x80x9cspiders,xe2x80x9d located at opposite ends of the drum. Each spider contains a centrally located bearing for rotatably supporting a drum axle, and a plurality of outwardly extending mechanical fiducials, e.g. bullet-shaped members, which are adapted to mate with complimentary structure, e.g., V-notched blocks, mounted on each work station to precisely locate and space the work-stations relative to the drum""s photoconductive surface. When it comes time to replace the image-recording and/or transfer drums, the work-stations are retracted from their respective positions adjacent the drum surface, thereby providing clearance for drum removal, and the entire drum assembly, including the spider members, are slid axially through an opening in the front wall of the printer frame. The entire drum assembly is then returned to the manufacturer""s facility where the assembly is disassembled and a new drum can be substituted for the worn drum. To install a new drum assembly, the reverse process is carried out, the drum assembly being moved axially inward into the printer frame, until the spiders engage and are seated upon the dowel pins. Thereafter, the workstations are moved toward the drum surface and their respective operative positions. In a similar manner, each of the individual work-stations may be removed from the printer housing, leaving behind, when the drum assembly has been removed, a frame that is totally void of any major components. Only the registration dowel pins remain in the frame, and the entire printer can be reassembled with great precision based on the location of these pins.
While the above-described apparatus fulfills the work station-registration needs for high quality color printing, it may be viewed as a relatively costly and labor-intensive solution. For example, to replace the drum surface, the entire drum assembly, which including the relatively costly drum-support members (spiders) and axles, must be replaced. This requires removal of a relatively heavy subsystem from the printer housing and shipment of such subsystem back to the manufacturing for refurbishing. Since most of the drum assembly components do not require replacement, these components undergo unnecessary shipping and handling during which time they may be damaged or have parts misaligned. This disadvantage is exacerbated by the weight of such components. Ideally, only those components of the drum assemblies that actually need replacement (typically the outermost layer of the drum) should be removed from the printer housing and the remaining components should stay in place for the life of the printer.
In view of the foregoing discussion, an object of this invention is to provide an improved system for precisely and repeatedly positioning the various workstations of an electrophotographic printer relative to an image recording and/or image-transfer drum.
Another object of this invention is to provide an improved document printer/copier in which a work station-registration and drum-support member comprising a drum assembly mounted within a printer/copier frame can be selectively de-coupled from the drum assembly and moved within the printer/copier frame to a location providing service access to the outer surface of an image-recording drum and/or image-transfer drum.
According to one aspect of the invention, a document printer comprises (i) a frame including a front frame plate, (ii) at least one reference pin or the like extending from the front frame plate at a predetermined location, (iii) an image-recording drum having an outer photosensitive surface and front and rear axles extending outwardly from opposing ends of the drum along an intended axis of rotation, (iv) a plurality of work-stations for producing transferable visible images on the drum""s photosensitive surface, and (v) a front drum-support member mounted on the front frame plate and precisely located thereon by the reference pin extending from the front frame plate, such front drum-support member having a set of mechanical fiducials for locating various work-stations relative to the drum surface. According to the invention, the front drum support member has a selectively energizeable clamping mechanism for selectively engaging a bearing on the front drum axle, whereby the front drum-support member can either rotatably support the front drum axle for rotation, or be decoupled therefrom so that the drum can be removed from the printer frame. Preferably, the front drum-support member is movably mounted on the front frame plate for movement between a first position in which its associated clamping mechanism is positioned to engage the bearing on the drum""s front axle, and a standby position in which the front drum-support member is sufficiently spaced from the drum""s front axle to enable servicing of the drum, e.g., to enable replacement of the drum""s outer photosensitive layer. Preferably, the printer of the invention further comprises an intermediate image transfer drum having opposing front and rear axles extending outwardly from opposite ends, and the front drum-support member is further provided with a second selectively energizeable clamp for selectively engaging a bearing on the front axle of the transfer drum. Also preferred is that the printer further comprises a rear drum-support member rigidly mounted on a rear frame plate of the printer frame and precisely located thereon by reference pin extending from the rear frame plate. Wherein this aspect of the present invention employs reference pins, other mechanical reference surfaces are envisioned such as a V-block, a flat surface, or a hole that mates with a member in the drum support member, which can all be used as a reference surface. Such rear drum-support member includes (a) a bearing for rotatably supporting the rear axle of the image-recording drum, and (b) a second set of fiducials that cooperate with the fiducials on the front drum-support member for locating the various work-stations of the printer relative to the drum surface. Preferably, the rear drum-support member comprises a selectively energizeable clamp, which serves to releasably and rotatably support the rear axle of the image-transfer drum.
According to another aspect of the invention, new drum-support members of the above type are provided. Rather than being an integral part of the drum assembly that stay with the drum assembly when it comes time to replace the drum surface, the drum-support members of the invention are adapted to remain in the printer housing while only the outer surfaces of the drum(s) are replaced or serviced. Preferably, the front drum-support member of the invention comprises a selectively energizeable clamp which, when energized, clamps about the outer race of an axle bearing that serves to rotatably mount the image-recording drum. When so clamped, the drum-support members become part of the drum assembly, and a plurality of reference fiducials located at predetermined positions about the periphery of the drum-support member serve to position the various workstations of the printer. When unclamped, the drum-support members are de-coupled from the drum(s). Mounting structure on the front drum-support member enables such member to be (i) slided axially (relative to the drum""s axis of rotation) to suitably displace the member from the drum, and (ii) pivoted to a location laterally spaced from the drum axis. According to a preferred embodiment, the front drum-support member further comprises a bearing for rotatably supporting one end of the image transfer drum in a cantilever fashion and a selectively energizeable clamp which, when energized, clamps about the outer race of an axle bearing serving to rotatably mount an image-transfer drum. Preferably, the rear drum-support member is adapted to be rigidly connected to the rear frame plate of the printer frame.
As indicated above, an advantageous technical effect of the invention is that the most significant technical benefits of the work-station registration scheme disclosed in the above-referenced U.S. application Ser. No. 09/474,352 have been preserved while the cost of implementing such a scheme is minimized by virtue of the fact that the most costly components of the drum assembly (i.e., the drum-support members (xe2x80x9cspidersxe2x80x9d) and drum axles) are never removed from the printer and can remain with the printer throughout its useful life. Another advantage of the invention is that the end user can gain access to the image recording and transfer drums for servicing without having to remove and replace relatively heavy sub-assemblies.
The invention and its advantages will be better understood from the ensuing detailed description of preferred embodiments, reference being made to the accompanying drawings in which like reference characters denote like parts.